Probes as thin as 0.007" diameter have been utilized for high density testing, however such high density probes are extremely expensive, have limited life cycle, and have a downward limit as to their center spacing and a minimum spring force. These spring contact probes must be installed in a fixture having sufficient room for drilling holes in a side by side array, inserting receptacles into the fixture holes and then inserting probes into the receptacles. Integrated circuit technology has progressed and resulted in integrated circuit packages becoming increasingly compact and complex, resulting in smaller packages and higher lead densities. Several techniques have been utilized for testing the circuit pads of printed circuit boards prior to installation of the integrated circuit package; these have been of several types, including the "bed of nails" fixture arrangement in which a matrix block is pre-drilled with a grid like array of holes. Receptacles and probes are positioned in the holes to conform to the test sites on the printed circuit board. Where an integrated chip package is to be mounted on the printed circuit board, the test fixture must be specially adapted for testing the IC test sites with even finer and more densely packed probe positions in those areas. The result of this is that when testing integrated chip pad positions on a printed circuit board, each fixture must be individualized.
The close center testing required for the pad test sites of printed circuit boards has been a significant problem to fixture manufacturers and users alike as the majority of printed circuit boards have mixed technology components fitted on the same matrix. Mixed technology refers to both conventional through board and surface mount technology components. With these different types of components, there is a variation of pitch between test pads, or space between test pads, which can vary from 0.100 to as little as 0.006 inch. This unavoidably increases the complexity of the test fixture. Standard test fixtures have a nine millimeter probe plate which accommodates the spring contact probe receptacle. Setting u this probe plate is a relatively simple procedure, providing that the test pad centers do not decrease below 0.050 inch pitch or spacing. If the center distance between pads is reduced from 0.050 pitch, due to including an IC package footprint on the circuit board for example, the fixture manufacturer must modify the probe plate. In the modification, accurate engineering modifications would have to be made and would include a reduction in the thickness of the probe plate material in the vicinity of close center test pads deemed necessary for test probe access. Another method is to construct a block, or probe matrix, and insert this into the standard probe plate. Both of these methods have their limitations and are extremely difficult to construct. The most commonplace problem generated by these modifications lies in the physical removal of probe plate material necessary to accommodate the matrix and the lack of side wall support for standard 0.100, 0.075 and 0.050 inch pitch probes to be mounted within close tolerance of this area.
Accordingly, an increasing need in the industry has been seen for a fixture arrangement which can easily and quickly be adapted to test the close pad pitches of high density integrated circuit packages. As integrated circuit packages become even smaller and more complex, the complexity of the task for the testing facility increases dramatically, quickly reaching a point where conventional spring contact probe technology can no longer be used. Therefore, what is desired is an arrangement for high density testing that can be easily and quickly adapted to different IC package configurations and in which the probe or conductor tips can be precisely aligned with the test site pads for an integrated circuit package.